1. Field of the Invention
This invention pertains generally to high-voltage breakers and more particularly to breakers employing a compressed-gas quenching medium.
2. Description of the Prior Art
In German Auslegeschrift 1,154,548, an electric circuit breaker is shown, wherein an electronegative, fluorine-containing gas, such as SF.sub.6, is used as a quenching and insulating medium. This breaker comprises two contacts which are movable with respect to each other and between which an arc is drawn when the breaker is opened. The contacts consist of carbon, preferably graphite, which keeps the destruction of the contacts and the formation of decomposition products low during the action time of the arc. The graphite contacts are made solid and are inserted into cup-shaped electrodes. The walls of the cup-shaped electrodes partly engage undercuts in the cylinder surface of the contacts.
In the case of high-voltage power circuit breakers, particularly compressed-gas breakers, it is advantageous to make the contacts hollow and nozzle-shaped. This facilitates the removal of the hot arc gases produced during the switching off process. The hollow contacts support at their end faces, arcing electrodes which, according to one arrangement, are made of annular shape. In this manner the contact system can satisfactorily withstand the hot arc gases.
The contact system normally includes at least one stationary, hollow, nozzle-shaped contact of arc-resistant material such as graphite, which is supported at one end thereof by an electrically conducting copper tube. In the closed position the stationary contact is surrounded by a movable, tubular switching member such as that described in U.S. Pat. No. 3,789,175. The latter includes a plurality of spring loaded contact elements which exert a spring force against the stationary contact to ensure a positive electrical connection.
One problem with the last-mentioned design occurs in opening the contacts. The spring loaded elements are drawn across the joint formed between the tube and the graphite nozzle. Because of the substantially lower conductivity of the graphite compared with that of copper, a voltage step is produced, which often times can exceed the magnitude of the cathode and anode drop. An arc develops between the copper tube and the contact elements, which causes burns at the run-off edge of the copper tube.
It is therefore a primary object of this invention to provide a stationary contact which achieves good arc resistance employing relatively simple and inexpensive means.
It is also an object of this invention to improve the commutation of the electric current from the conducting tube to the nozzle body.